Method for collecting platelets and other blood components from whole blood

ABSTRACT

A method for collecting, from whole blood, platelets suspended in plasma. By centrifuging the blood at a high enough rotational speed, the platelets are separated from the plasma and the red blood cells. In a preferred embodiment, some of the plasma is removed while the centrifuge is being spun to keep the platelets separated from the plasma. Then, the speed of rotation is altered so as to cause the platelets to mix with the remaining plasma. The platelets can then be collected with the remaining plasma.

TECHNICAL FIELD

This invention generally relates to systems and methods for processingblood and other biological fluids.

BACKGROUND ART

FIG. 1 shows a typical disposable bag set used in the prior art tocollect platelets from whole blood. The set includes a needle 10 orcannula, which is inserted into a vein of a donor. The needle 10 isconnected to the tube 11, which in turn is connected to collection bag12, so as to allow whole blood to flow from the donor through the needle10 and the tube 11 into collection bag 12. The collection bag 12contains anticoagulant. After the desired amount of blood has beencollected into collection bag 12, the needle 10 is removed from thedonor, and tube 11 is cut and heat sealed. The remainder of the bag setis then brought to a centrifuge, which spins the bag set so that theblood in collection bag 12 separates into platelet-rich plasma and redblood cells. Typically, the centrifuge is not located at the point wherethe blood donation takes place.

After the blood has separated into platelet-rich plasma and red bloodcells (RBCs), the bag set is removed from the centrifuge. Theplatelet-rich plasma is urged from collection bag 12 through tube 13into platelet-storage bag 14. The tube 13 leading to the platelet- andplasma-storage bags 14, 15 is then cut and heat sealed. Storage-solutionbag 16 holds RBC-storage solution. After the platelet-rich plasma hasbeen urged into the platelet-storage bag 14, the RBC-storage solution isurged from the storage-solution bag 16 into the collection bag 12. Thetube 41 connecting the collection and storage-solution bags 12, 16 isthen cut and heat sealed.

At this stage, the bag set has been divided into two portions: (i) thefirst portion consists of the collection bag 12, which now holdsprimarily red blood cells (along with storage solution), filter 17,RBC-storage bag 18, and the tubing 19 that connects these components,and (ii) the second portion consists of the platelet-storage bag 14,which now holds platelet-rich plasma, and the plasma-storage bag 15 andthe tubing that connects these two components.

The first portion may be hung, so that gravity causes the RBC componentto pass from the collection bag 12 through the filter 17 to RBC-storagebag 18. The filter 17 removes white blood cells (WBCs) from the redblood cells. After the red blood cells (and storage solution) pass intothe RBC-storage bag 18, tube 19 is cut and heat sealed.

To collect platelets, the second portion is centrifuged at a highrotational speed in order to separate the platelets from the plasma.After the platelets have been separated from the plasma, some of theplasma is urged from the platelet-storage bag 14 into the plasma-storagebag 15. Typically, 50 mls of plasma are left with the platelets in theplatelet-storage bag 14. After the desired amount of plasma has beenremoved from the platelet-storage bag 14 to the plasma-storage bag 15,the tube connecting these two bags is cut and heat sealed. Thus, at theend of the procedure, the platelet-storage bag 14 holds platelets inabout 50 ml of plasma, the plasma-storage bag 15 holds platelet-poorplasma, and the RBC-storage bag 18, of course, holds red blood cells.

This prior-art process of collecting and separating blood componentsinvolves many steps and frequent human intervention. The arrangement ofthe prior-art bag set does not permit the process to be easilyautomated.

SUMMARY OF THE INVENTION

The present invention is directed to systems and methods for collecting,from whole blood, platelets suspended in plasma. By centrifuging theblood at a high enough rotational speed, the platelets are separatedfrom the plasma and the red blood cells. In a preferred embodiment, someof the plasma is removed while the centrifuge is being spun to keep theplatelets separated from the plasma. Then, the speed of rotation isaltered so as to cause the platelets to mix with the remaining plasma.The platelets can then be collected with the remaining plasma.

A system that may be used for carrying out the invention includes acentrifuge rotor, a flow-control arrangement and a spinner. Theflow-control arrangement introduces whole blood into the centrifugerotor and removes blood components from the centrifuge rotor. Acontroller causes the spinner to rotate at two different speeds: Therotor is spun at a first speed so as to separate the blood into a firstcomponent, a second component and a third component. The first componentis primarily plasma. The second component is located, while the rotor isbeing spun, outside of the first component and is primarily red bloodcells. The third component is located, while the rotor is being spun,between the first and second components and includes platelets. Thecontroller causes the rotor's speed of rotation to be altered so as tocause the third component to mix with the first component. Thecontroller also causes the flow-control arrangement to remove from therotor a portion of the plasma containing platelets.

As noted above, in a preferred embodiment, the controller causes theflow-control arrangement to remove some of the first component (theplasma) before the third component (comprising the platelets) is mixedwith the first component. The system also preferably includes aplasma-volume determination sensor in communication with the controller;the plasma-volume determination sensor determines the volume of thefirst component in the rotor. The controller may thus remove a portionof the first component based on the determined volume of the firstcomponent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a disposable set that may be used in a prior-art system forcollecting platelets from whole blood.

FIG. 2 shows a cross-sectional view of a variable-volume rotor mountedin a chuck that spins the rotor and causes the rotor's volume to change.

FIG. 3 shows a disposable set using a variable-volume rotor, such as theone in FIG. 2.

FIG. 4 shows a control unit holding the disposable of FIG. 3.

DESCRIPTION OF SPECIFIC EMBODIMENTS

A method of collecting platelets is described in connection with FIG. 2.FIG. 2 shows a cross-section of a rotor 21 mounted in a chuck 80, whichis located in the control unit and which holds the rotor 21. This rotor21 may be any one of a variety of designs, but preferably the rotor hasa variable total volume, such as the rotors shown and described in U.S.Pat. No. 5,733,253 (which is incorporated herein by reference). (Therotor shown in FIG. 2 is similar to the rotor shown in FIGS. 1-4 of U.S.Pat. No. 5,733,253, but it will be appreciated that other designs, suchas other designs shown in U.S. Pat. No. 5,733,253, may be used instead.)A motor 81 causes the chuck 80 and the rotor 21 to spin. The controlunit also includes a pump 83, which is connected through the cannulatedaxis 82 of the motor 81 to the interior of the chuck 80. The rotor 21has an elastic diaphragm 70, which defines the interior volume of therotor 21. Upper boundary wall 72 also defines the interior volume of therotor 21. The position of the diaphragm 70 determines the volume of therotor, and the position of the diaphragm 70 may be controlled bycontrolling, by means of the pump 83, the pressure of the gas in theinterior of the chuck 80. The interior of the chuck 80 includes one ormore apertures 84 to permit the gas to come into fluid communicationwith the diaphragm 70. The rotor 21 may also include a interior wall 75with perforations 71. The boundary wall 72 and the interior wall 75 forma passage 73, through which blood and blood components may flow to andfrom the rotor's non-rotating portion 74 and the tubing 33 attached tothe rest of the disposable set. A rotary seal 76 provides a seal betweenthe rotating and non-rotating portions of the rotor 21. In lieu of theperforated interior wall 75, channels may be located on the interiorsurface of the boundary wall 72 to provide fluid communication betweenthe rotor's non-rotating portion 74 and the outer radius of the rotor'sinterior (as shown in FIGS. 41 and 42 of above-referenced U.S. Pat. No.5,733,253).

FIG. 2 shows the rotor 21 at its maximum volume, with the diaphragm 70stretched as far as the chuck 80 permits it to be stretched. The rotor21 is spun sufficiently fast by the chuck 80 and the motor 81 to causethe blood to be separated into red blood cells 93, platelets 92 andplasma 91. Since, of these three blood components, the RBC component 93of the blood has the greatest specific gravity, the RBC component is thefurthest from the rotor's axis of rotation. The plasma component 91 hasthe lightest specific gravity, and therefore the plasma component is theclosest to the axis of rotation. The platelet component 92, having anintermediate specific gravity, forms a thin layer between the plasma andRBC components.

In order to collect the platelets, it is preferable first to collect allbut about 50 milliliters of the plasma. The remaining 50 mls of plasmawill be used to store the platelets, as the standard practice in theindustry is to store a unit of platelets in 50 mls of plasma. The plasma91 is collected (i.e., urged through fixed portion 74 to tube 33) bycontinuing to spin the rotor 21 and using the pump 83 to increase thepressure against the diaphragm 70, and/or by slowing the revolutions ofthe rotor 21. The rotor 21 should preferably continue to be spun quicklyand smoothly enough to keep the platelets 92 in a separate layer.

Once all but 50 mls of plasma 91 has been collected, the platelets 92may be mixed with the remaining plasma by sharply changing the speed ofrotation of the rotor 21. It has been found that, by sharply changingthe rotor's speed of rotation, the platelets will mix with theneighboring plasma. Because the red blood cells have a much heavierspecific gravity, the red blood cells tend to remain in their separatelayer. Of course, the rotor's speed must not be altered so radically andquickly as to cause the red blood cells as well to mix with the othercomponents. Alternatively, the speed of rotation may be slowedsufficiently—although not necessarily sharply—so that the platelets mixwith the plasma but the red blood cells remain separate. Once theplatelets are mixed with the remaining plasma, additional pressure maybe created by the pump 83 to push the diaphragm 70 further outward andforce the platelets, now suspended in plasma, out of the rotor into tube33. The red blood cells may then be collected. Each of the components,platelets suspended in plasma, platelet-poor plasma, and the red bloodcells should be directed to a separate container. Alternatively, one orboth of the platelet-poor plasma and the red blood cells may be returnedto the donor.

FIG. 3 shows a disposable set that may be used in theplatelet-collection process just described. The disposable set includesthe rotor 21, a plasma-storage container 24, a platelet-storagecontainer 99, a RBC-storage container 28, a filter 17 for removing whiteblood cells from the red blood cells, a cannula 10 (or other means forpermitting whole blood to enter the disposable set), and tubing 33connecting these components. The plasma-storage container 24 may containanticoagulant, which may be introduced into the whole blood as it isbeing drawn through the needle 10 to the rotor 21. The platelet-storagecontainer 99 may contain platelet-storage solution, and the RBC-storagecontainer 28 may contain RBC preservative. After the plasma and theplatelets have been removed from the rotor 21, the RBC preservative maybe urged from the RBC-storage container 28 into the rotor 21, where theRBC preservative is mixed with the red blood cells remaining in therotor 21. The red blood cells and the preservative may then be urgedfrom the rotor 21 through the filter 17 into the RBC-storage container28, in the manner described in concurrently filed application, Ser. No.09/271,594, for a “System and Method for Separating Blood Components,”and listing Headley and Powers as inventors. (This application isincorporated herein by reference.) Alternatively, the present inventionmay be used with the system and process described in concurrently filedapplication, Ser. No. 09/271,627, for a “System and Method forRed-Blood-Cell Apheresis,” and listing James Cianci as the inventor.(This application is also incorporated herein by reference.)

FIG. 4 shows the disposable set of FIG. 3 mounted in a control unit 20.The control unit 20 includes a flow-control arrangement for controllingand/or causing flow between the needle 10, the rotor 21 and the storagecontainers 24, 99, 28. The flow-control arrangement may include valves22, 23, 98, 27, which control the flow through the various branches ofthe tubing. Alternatively, a single valving cassette may be used tocontrol the flow through the various branches of the tubing. Forinstance, applying a vacuum on the rotor's diaphragm while valve 22 isopen helps draw blood from the donor into the rotor 21. In addition toor in lieu of changing the pressure against the rotor's diaphragm, thecontrol unit may be provided with independent pumping mechanisms (suchas a peristaltic pump) that act on the tubing (or on a valving cassette)to force fluid through the tubing in the desired direction.

In order to determine how much plasma should be removed in order toleave only 50 mls of plasma, in which the platelets are to be suspended,the control unit may be provided with an arrangement for determining thevolume of the red blood cells. One means of determining the volume ofthe red blood cells is to provide an array 97 of optical sensors (shownin FIG. 2) in the chuck 80 to determine the radius of the inner boundaryof the red blood cells 93 when the blood has been centrifuged intodifferent components. (If the boundary wall 72 is translucent, the arraymay be mounted above the rotor 21 instead of below it.) The control unit20 may then calculate the volume of the red blood cells based on thelocation of this boundary when the rotor is filled with, say, one unitof blood. Using this volume information, the control unit may determineapproximately the weight of the red blood cells in the rotor, based onthe specific gravity of red blood cells.

By weighing the chuck/rotor combination before and after the whole bloodwas introduced into the rotor, the control unit may determine the weightof all the blood components in the rotor when the rotor is filled. Bysubtracting the weight of the red blood cells from the total weight ofall the blood components in the rotor, the control unit may determineapproximately the weight of the plasma in the rotor, and how much of itshould be removed in order to leave approximately 50 mls of plasma inthe rotor. By weighing the chuck/rotor combination as platelet-poorplasma is being urged from the rotor, or alternatively by weighing thecontainer 24 that holds the plasma as it leaves the rotor, the controlunit can stop removing plasma when the correct amount of plasma has beenremoved. The platelet-poor plasma is preferably directed to theplasma-storage container 24.

At that point, there should be approximately 50 mls of plasma left inthe rotor, as well as all the platelets and all the red blood cells. Thespeed of the rotor may then be changed rapidly, in order to cause theplatelets 92 to become mixed in the approximately 50 mls of the plasmaremaining. The platelet/plasma combination is then urged from the rotorand sent to the platelet-storage container 99. Another optical sensor96, mounted on the outlet tube 33 senses when the red blood cells startemerging from the rotor. (See FIG. 4.) When the red blood cells aredetected, flow to the platelet-collection container 99 is stopped, andthe red blood cells may be directed through filter 17 to aRBC-collection container 28.

Although the invention has been described with reference to severalpreferred embodiments, it will be understood by one of ordinary skill inthe art that various modifications can be made without departing fromthe spirit and the scope of the invention, as set forth in the claimshereinbelow.

What is claimed is:
 1. A method of collecting platelets comprising:providing a centrifuge rotor having a variable total volume; introducingwhole blood into the centrifuge rotor; determining a weight of the wholeblood introduced into the rotor; spinning the rotor at a first speed soas to separate the blood into a first component, a second component anda third component, wherein the first component is primarily plasma,wherein the second component is located, while the rotor is being spun,outside of the first component and is primarily red blood cells, andwherein the third component is located, while the rotor is being spun,between the first and second components and includes platelets; removingfrom the rotor a weight of first component; determining as a function ofthe weight of the whole blood, the weight of first component to remove;changing the rotor's speed of rotation so as to cause the thirdcomponent to mix with first component remaining in the rotor; andremoving from the rotor a portion of the plasma containing platelets. 2.The method of claim 1 wherein determining a weight of the whole bloodcomprises weighing the centrifuge rotor before and after introducing thewhole blood.
 3. The method of claim 1 wherein removing a weight of firstcomponent further comprises weighing the removed first component.
 4. Themethod of claim 1 wherein removing a weight of first component furthercomprises weighing the centrifuge rotor as the first component isremoved to measure the amount of first component that has been removed.5. The method of claim 1 further comprising approximately determiningweight of red blood cells in the rotor during said spring at the firstspeed.
 6. The method of claim 5 wherein approximately determiningcomprises sensing volume of red blood cells in the rotor and calculatingweight of red blood cells from the volume based on specific gravity ofthe red blood cells.
 7. The method of claim 5 wherein determining theweight of first component comprises calculating the amount of firstcomponent to remove so as to leave a desired amount of plasma in therotor, the calculation being a function of the given weight of the wholeblood and the determined weight of the red blood cells.
 8. A method ofcollecting platelets from whole blood, the method comprising: providinga disposible set having an inlet, a platelet container, a centrifugerotor having a variable total volume, and tubing connecting the inlet,the platelet container and the rotor; providing a control unit having aspinner in which the rotor may be held; placing the rotor in thespinner; drawing whole blood through the inlet; directing the wholeblood from the inlet through the tubing to the rotor; determining aweight of the whole blood directed into the rotor; causing the spinnerto rotate the rotor so as to separate the whole blood into a firstcomponent, a second component and a third component, wherein the firstcomponent is primarily plasma, wherein the second component is located,while the rotor is being spun, outside of the first component and isprimarily red blood cells, and wherein the third component is located,while the rotor is being spun, between the first and second componentsand includes platelets; removing from the rotor a weight of firstcomponent determining as a function of the weight of the whole blood theweight of first component to remove; altering the rotor's speed ofrotation so as to cause the third component to mix with the firstcomponent; and urging a mixture of the first and third components out ofthe rotor, while the rotor is still spinning.
 9. The method according toclaim 8, wherein whole blood is drawn through the inlet and directed tothe rotor while the rotor is mounted in the spinner.
 10. The methodaccording to claim 9, wherein the centrifuge rotor is provided with afixed portion, a rotatable portion and a rotary seal providing a sealbetween the fixed and rotatable portions, and the tubing is connected tothe rotor's fixed portion.
 11. The method according to claim 10, whereinthe control unit varies the volume of the centrifuge rotor.
 12. Themethod according to claim 11, wherein the centrifuge rotor is providedwith a flexible diaphragm which defines the volume of the rotor, and thecontrol unit is provided with means for varying air pressure adjacentthe flexible diaphragm so as to vary the total volume of the centrifugerotor.
 13. The method according to claim 8, wherein the centrifuge rotoris provided with a fixed portion, a rotatable portion and a rotary sealproviding a seal between the fixed and rotatable portions, and thetubing is connected to the rotor's fixed portion.
 14. The methodaccording to claim 8, wherein the disposable set includes aplasma-storage container and an RBC container, the method furthercomprising: directing a portion of the first component to theplasma-storage container and the third component to the RBC container.15. The method according the claim 8, wherein the disposable setincludes return means, the method further comprising: directing at leastone of the first and second components back to a whole blood donorthrough the return means.